There is a permanent need in the industry of exploration and production of oil and gas from earth formations for monitoring and surveillance of operations involving the earth formations. Particularly, it has many benefits to be able to monitor changes in hydrocarbon reservoirs within the earth formation over time which may be introduced as a result of producing hydrocarbon fluids from the hydrocarbon reservoirs and/or as a result of injecting fluids into the hydrocarbon reservoirs.
In one monitoring system commercialized by CGG, sometimes referred to by the name SeisMovie™, buried seismic source and receiver installations are employed, which has the advantage that sources and receivers can be positioned below weathering layers which are subject to seasonal variation. This system is therefore suitable for 4D monitoring of a weak 4D signal over long periods of time spanning several seasonal cycles. Reference is made to a brochure from CGG Veritas titled “SeisMovie, continuous high-resolution reservoir monitoring.” The sources are piezoelectric vibrator sources positioned within vertical boreholes.
A drawback of the known SeisMovie™ system is high cost as multiple seismic sources are permanently buried. Furthermore, the burying of the sources and the receiver network is associated with a large environmental imprint.